Rock crushers such as cone crushers are generally used for crushing large rocks into smaller rocks or gravel. These machines typically include, among other components, a stationary inverted conical- or bowl-shaped bowl that is coupled to a bowl liner and a cone assembly that is disposed within the bowl liner and is typically gyrated within the bowl liner during rock crushing operations. The bowl liner includes an opening at the top of the bowl where, for example, rocks may pass. The gyrating motion of the cone assembly results from the rotational motion of an eccentric, which rotates about a center axis. This center axis also generally defines the center axis of the rock crusher machine. The cone assembly will typically be defined by its own center axis, for purposes of this description to be called a “cone axis,” which is offset from the center axis of the rock crusher.
As described above, during a typical rock-crushing operation, the cone assembly moves in a gyrating motion within the interior space of the bowl liner. During operation, the cone axis of the cone assembly will rotate around the center axis of the rock crusher machine (e.g., the center axis of the cone assembly will be offset from center axis of the rock crusher) in a gyrating motion. The gyratory motion of the cone assembly may be imparted via an eccentric that rotates with respect to a stationary or movable shaft. In either case, a frame supports the shaft and cone assembly, and a drive shaft or other driving mechanism is utilized to drive the eccentric assembly. When the rock crusher is operating normally and crushing rocks, the cone assembly rotates in a direction opposite to the eccentric direction of rotation due to the countervailing forces of the material (e.g., rocks) being crushed.
The eccentric typically rotates at a high rate of speed, in some cases, at speeds greater than or equal to about 200 rotations per minutes (rpm). Although the interface between the eccentric and the cone assembly is lubricated and generally includes bearings and/or bushings disposed between the two components, without counteracting forces preventing movement, the cone assembly will tend to rotate along with the eccentric. For example, during no-load operations when the eccentric is rotating but no material is being crushed, the cone assembly along with the cone shaft tends to accelerate in the direction of the eccentric. Eventually, if no material is dropped into the crusher and the cone assembly is allowed to rotate freely with the eccentric, the tendency is for the cone assembly to spin at the same high rate of speed as the eccentric. Such rotation is generally undesirable because if rocks are suddenly introduced into the crusher, certain crusher components could be damaged. These components include, for example, the mantle that covers the cone assembly and the bearings that are disposed between the eccentric and the cone assembly. The abrupt introduction of rocks onto the fast moving mantle can result in friction damage to the mantle. The sudden deceleration and reversal of direction of rotation of the cone may cause bearing elements to skid on adjacent surfaces if the lubrication film is momentarily disrupted. Such skidding action may cause premature wear and/or permanent damage to the bearing element(s) and/or bushings.
Further, under certain circumstances, the cone assembly may be subjected to torque(s) in the direction of eccentric rotation that are significantly higher than those produced during normal no-load conditions. Such torque may be the result of uncrushable objects entering the crushing chamber and/or excessive internal friction within the crusher.